In an unprecedented slap at President George W. Bush's war policy, the U.S. Congress approved legislation that links withdrawal of combat troops from Iraq to paying for the war, ensuring a veto.

The news comes as Prince Harry prepares to go to the war-torn country, insisted he is not afraid to die in Iraq.

By a vote of 51-46, the Senate yesterday joined the House of Representatives in backing the bill that would provide about $100 billion (£50 billion) for the wars in Iraq and Afghanistan this year while setting a deadline to withdraw U.S. forces from Iraq over the next 11 months.

It was the first time that the entire Congress, controlled by Democrats since January, has defied the president.

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Meanwhile top U.S. commander in the region General David Petraeus has said things will get worse in Iraq before they get better.

"My sense is that there would be an increase in sectarian violence, a resumption of sectarian violence, were the presence of our forces and Iraqi forces, at that time, to be reduced," Petraeus told reporters at the Pentagon.

He said the new effort to curb violence with more troops, ordered by Bush in January, meant going into neighborhoods where extremists had been able to operate freely.

"Because we are operating in new areas and challenging elements in those areas, this effort may get harder before it gets easier," said Petraeus, who has briefed Bush and members of Congress on the war during his visit to Washington.

"I think there is the very real possibility that there's going to be more combat action and that, therefore, there could be more casualties," he said.

Bush has repeatedly said he will not accept "surrender" dates.

"The president will veto this legislation," White House spokeswoman Dana Perino said. "The president is determined to win in Iraq. The bill they sent us today is mission defeated."

Democrats might arrange to deliver their bill to the White House on Tuesday, the fourth anniversary of Bush declaring aboard the USS Abraham Lincoln: "Major combat operations in Iraq have ended".

The aircraft carrier was decorated with a large "mission accomplished" banner.

Calling for a "new direction in Iraq," Senate Appropriations Committee Chairman Robert Byrd, a West Virginia Democrat, said U.S. troops "had the courage and the strength to win the war, but the president has not had the wisdom to win the peace."

Democrats, however, doubt they have two-thirds support in Congress to overturn a presidential veto. The House passed the bill on Wednesday 218-208 on a mostly partisan vote.

If there is a veto and it is not overturned, lawmakers would likely craft another bill sending money to the troops in Iraq, possibly with some watered-down conditions that Bush could accept, and leave the withdrawal fight for the future.

Just two Republican senators voted for the withdrawal bill, but Democrats hope that as 2008 elections approach, more Republicans will join the push to wind down the war.

Indeed, one Republican who voted against the bill warned she did not support an open-ended commitment.

"If the president's new strategy does not demonstrate significant results by August, then Congress should consider all options including a redefinition of our mission and a gradual but significant withdrawal of our troops next year," Senator Susan Collins of Maine, who is up for re-election in 2008, said in a statement.

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Opponents of the bill passed by the House and Senate said it would make a difficult situation in Iraq worse. Senator Joseph Lieberman of Connecticut, a Democrat-turned-independent, said removing combat troops "makes no military or strategic sense."

With this legislation, Democrats are asserting Congress' oversight of the 4-year-old war that has killed more than 3,300 U.S. troops. The bill presents Bush with several tough conditions he has resisted.

The Pentagon would have to begin withdrawing combat troops from Iraq by October 1 at the latest, with the aim of finishing the redeployment in six months. The March 31 deadline is nonbinding, though, leaving it up to Bush and his generals.

With the U.S. military now stretched thin, the bill tries to ensure troops are not sent into combat without proper rest, training and equipment.

Bush could waive the mandate, which could be politically embarrassing.

Like the House, the Senate engaged in an emotional debate on the war.

Byrd, a staunch opponent of the Iraq war, accused Bush of trying to "scare the pants off the public by suggesting that our bill could result in death and destruction in America. What utter nonsense. What hogwash."

Bush has said that setting exit dates would undermine troops and allow enemies to make Iraq a base from which to attack the United States.

Senate Armed Services panel Chairman Carl Levin, a Michigan Democrat, countered that the bill required "the beginning of a partial reduction of U.S. troops, leaving time for Iraqis to make the political compromises they promised to make months ago."

After the House passed the bill, Democratic Rep. John Murtha of Pennsylvania sketched out the way forward on this dispute. He said House Democrats are preparing two post-veto options: A two-month war funding bill, or a bill providing combat funds through September 30, the end of the fiscal year.

As now written, neither option calls for withdrawing troops by specific dates. But both would set benchmarks for gauging progress in stabilizing Iraq.